Lymnaea epidermal growth factor promotes axonal regeneration in CNS organ culture

Members of the epidermal growth factor (EGF) family are frequently implicated in the injury response of the mammalian nervous system. Although this implication is supported by extensive molecular evidence, it is not underpinned by conclusive functional data. Recently, we found that expression of an EGF homolog from the pond snail Lymnaea stagnalis (L-EGF) is upregulated after axotomy in the adult CNS, suggesting a role for this molecule in the injury response of the CNS. In the present study we asked whether L-EGF can promote axonal regeneration of three types of identified neurons in organ-cultured CNS. Treatment with purified L-EGF substantially enhanced axonal regeneration of all three types of neurons, an effect inhibited by submicromolar doses of PD153035, a specific EGF receptor (EGFR) tyrosine kinase inhibitor. In addition, PD153035 and K252a, a nonspecific kinase inhibitor, also reduced the degree of axonal regeneration that occurs without L-EGF supplementation, indicating that L-EGF or other EGFR ligands synthesized in the CNS participate in the regenerative response. An intriguing aspect of these results is that axonal regeneration of different, intrinsically L-EGF responsive and unresponsive neurons occurred in a coordinated manner. This observation suggests that indirect in addition to direct actions contribute to the beneficial effect of L-EGF. In conclusion, we provide functional evidence that an EGF homolog can promote axonal regeneration, substantiating existing molecular evidence implicating the EGF family in peripheral nerve regeneration and emphasizes the therapeutic potential of these molecules.